Coincidentally Wiesbaden isn't only a beautiful place (not only) to learn about Social Business activities, but also the capital of the former Dukedom of Nassau. To this day, the reigning Grand Duke of Luxembourg also bears the title of the Duke of Nassau. Guillaume bears the title Hereditary Prince of Nassau.
Wiesbaden is a leader in the developing field of social business. Guillaume was accompanied by a delegation from the Sustainable Development Unit of the University of Luxembourg. The visit was part of Luxembourg's ongoing commitment to studying and developing methods of social business that can be implemented in the Grand Duchy.
The Cour Grand Ducal has kindly published a few pictures of the event on their website. Three newspaper articles can be found in the local newspaper, here , here and here. You may also find an English language summary on myMosaik.
Guillaume and his father paid an official visit to Wiesbaden in 2006. Tom Wagner has a gallery of photos of the 2006 visit, featuring a very different looking Guillaume.
Sources: Cour Grand Ducale, Wiesbadener Kurier, Wiesbadener Tageblatt, myMosaik, Tom Wagner